1. Field of the Invention
The present invention relates to a throttle apparatus for an internal combustion engine.
2. Description of Related Art
For instance, Japanese Unexamined Patent Publication No. 2009-185679A teaches a throttle apparatus that has a valve, an opening degree of which is adjusted by a drive motor to change a quantity of intake air supplied to an internal combustion engine.
Specifically, with reference to FIG. 6, the throttle apparatus 100 of Japanese Unexamined Patent Publication No. 2009-185679A includes a throttle body 102, the valve 103, a return spring 106, the motor 105, a plurality of output force transmission gears 107, a full close position stopper 134 and an intermediate position stopper 140. The throttle body 102 forms an intake passage, which conducts the intake air and is connected to the internal combustion engine. The valve 103 is rotatably received in the intake passage to change an opening degree of the intake passage. The return spring 106 urges the valve 103 from both of a full open position side and a full close position side of the valve 103 toward a predetermined intermediate position between a full close position and a full open position of the valve 103. The motor 105 drives the valve 103 in the opening direction (toward the open side) or in the closing direction (toward the close side) against the urging force of the return spring 106. The output force transmission gears 107 transmit the output force of the motor 105 to the valve 103. The full close position stopper 134 is adapted to engage with a valve gear 126, which is one of the output force transmission gears 107, when the valve 103 is driven in the closing direction (toward the close side) and reaches the full close position. The intermediate position stopper 140 is adapted to engage with the return spring 106 when the valve 103 is placed on the full close position side of the intermediate position.
The full close position stopper 134 receives the full close side engaging force, which is applied from the valve gear 126 at the time of engaging with the valve gear 126, at a point Q of action in the left-to-right direction in FIG. 6. The intermediate position stopper 140 receives an intermediate reaction force from the return spring 106 through the engagement with the return spring 106 at a point P of action in the top-to-bottom direction in FIG. 6.
The intermediate reaction force is always applied to the intermediate position stopper 140 in a range of valve opening degree (a valve opening degree range), which is equal to or smaller than an intermediate valve opening degree and in which the valve 103 is most frequently operated. Therefore, in a case where the throttle body 102 is made of a resin material, which has a low modulus of elasticity, a creep deformation tends to occur at the intermediate position stopper 140. Thus, a deviation in a relative position between the point P of action of the intermediate reaction force at the intermediate position stopper 140 and the point Q of action of the full close side engaging force at the full close position stopper 134 is likely to occur. Specifically, the point P of action of the intermediate position stopper 140 irreversibly moves toward the close side (top side in FIG. 6) upon deformation thereof while the point Q of action of the full close position stopper 134 is kept still without movement. Therefore, at the time of fully closing the valve 103, when the valve 103 is moved from the intermediate position to the full close position, the valve gear 126 may hardly collide against the full close position stopper 134 in some cases.